This application relates generally to gas turbine engine assemblies and more particularly, to turbine rotor blade airfoil profiles.
In the design, fabrication, and use of turbofan engine assemblies, there has been an increasing tendency towards operating with higher temperatures and higher pressures to optimize turbine performance. In addition, as existing turbine rotor blade airfoils reach the end of their useful life cycle, replacement of the airfoils with redesigned airfoils is often necessary to accommodate the higher temperatures and higher pressures. Moreover, airfoil redesign is desirable without altering or changing other parts of the turbofan engine assemblies.
At least some known rotor blade airfoils are exposed to hot combustion gases. For example, some known turbofan engine assemblies include a combustor that is upstream of a high-pressure turbine. Combustion gases discharged from the combustor flow past the rotor blades. As a result of their exposure to hot combustion gases, such blades may be subjected to high stress and high temperatures caused by thermal gradients and mechanical loadings in the blades. Over time, because of continued exposure to the combustion gases, such blades may bow, creep, and/or crack thereby reducing the operating performance of the engine.
During the design process, the shape of each rotor blade airfoil, as defined by the camber length, chord length, leading edge incident angle, trailing edge exit angle, and trailing edge thickness is variably selected to produce an optimized airfoil design based on the design constraints of the turbofan engine assembly in which the blades are employed. Optimally, the rotor blade airfoil is designed to provide peak performance without sacrificing the aeromechanical integrity of the rotor blade. Often, the design constraints require balancing. For example, longer airfoil chord lengths may negatively impact the life of rotor blades by moving natural frequencies of the blades into an operating range of the turbofan engine assembly at selected operating speeds as compared to shorter airfoil chord lengths. However, in contrast, shorter rotor blade chord lengths may negatively impact performance of the high-pressure turbine as compared to longer airfoil chord lengths.
In addition, other operating constraints may affect the design process. For example, at least some known high-pressure turbine rotor blades are subjected to natural frequency modes that may cause blade damage. More specifically, such frequency modes may cause the high-pressure turbine rotor blades to resonate which may cause cracking, trailing edge deterioration, corner loss, downstream damage, performance losses, reduced time on wing, and/or high warranty costs. In particular, some of such rotor blades may be especially prone to overall aerodynamic loss and high strains in blade regions at 20-30% span near trailing edge regions.